1. Field of the Invention
This invention relates to piezoelectric ceramic materials which are effectively utilizable in various types of actuators and which are composed of ternary solid solutions having a fundamental composition of Pb(Y.sub.1/2 Nb.sub.1/2)O.sub.3 -PbTiO.sub.3 -PbZrO.sub.3.
2. Description of the Prior Art
Piezoelectric ceramic materials used in actuators should have various characteristics such as a high piezoelectric constant, a high Curie point and high mechanical strength. One piezoelectric material which has been most widely used at present is a piezoelectric ceramic material composed of a ternary solid solution of Pb(Y.sub.1/2 Nb.sub.1/2)O.sub.3 -PbTiO.sub.3 -PbZrO.sub.3. Many studies have been made on the above ceramic material in order to further improve the characteristics mentioned above. For instance, in order to improve the mechanical strength, there were proposed ceramic materials in Japanese Unexamined Patent Publication No. 57-208183 in which part of Pb in the solid solution was substituted with Ba, Sr, Ca or the like and 0.1 to 1.0 wt% of In.sub.2 O.sub.3, MgO, Sb.sub.2 O.sub.3 or the like was added thereto.
The improvement in the strength of piezoelectric ceramic materials is needed especially when thin plates of piezoelectric ceramic materials are used in ultrasonic transducer elements or circuit elements. However, when thin plates of piezoelectric materials are laminated for use as actuators, it is desirable to increase the degree of the displacement of piezoelectric ceramic materials upon application of an electric field as large as possible rather than to improve the mechanical strength thereof by improving the piezoelectric constant of the materials.